Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$36.33	11.756%	$40.601	$40.60	$40.60	$40.60
Purchase #2	$167.97	12.213%	$188.4842	$188.48	$188.50	$188.50
Purchase #3	$166.74	7.848%	$179.8258	$179.83	$179.85	$179.80
Purchase #4	$69.68	7.846%	$75.1471	$75.15	$75.15	$75.10
Purchase #5	$154.58	10.105%	$170.2003	$170.20	$170.20	$170.20
Purchase #6	$56.62	9.405%	$61.9451	$61.95	$61.95	$61.90
Purchase #7	$53.51	11.281%	$59.5465	$59.55	$59.55	$59.50
7 purchase totals =	$705.43		$775.7500	$775.76	$775.80	$775.60